MORPHOLOGICAL STUDIES. 
71 
in different individuals. I have only seen black pigment on it 
in three Ammocoetes, while the majority of the adult Petro- 
myzon I examined had such pigment in a greater or less 
degree. I am hence forced to abandon as unlikely the idea 
that black pigment is formed in the larva, that it then gives 
place to white, and again in the adult a reversion to black 
occurs. This seems to me now unlikely, and the only conclu- 
sion I can draw is that the pigment is very variable, but that 
as a rule sooner or later black pigment is formed in the 
parietal eye of the Cyclostomata. 
List of Writers Cited. 
1. Ahlborn, F. — “Untersuchungen fiber das Gehirn der Petromyzonten,” 
‘ Zeitschr. f. wiss. Zool.,’ Bd. xxxix, Heft 2, p. 191, 1883. 
2. Aiilborn, F. — “Ueber die Bedeutung der Zirbeldriise,” ‘Zeitschr. f. 
wiss. Zool.,’ Bd. xl, Heft 2, p. 331, 1881. 
3. Beard, J. — “ The Parietal Eye in Fishes,” * Nature,’ No. 921, July 11th, 
1887, p. 216; August 11th, No. 928. 
1. Beraneck, E. — “Ueber das Parietal Auge der lleptilien,” ‘Jenaische 
Zeitschr. f. Naturwiss.,’ Bd. xxi, Hefte 3 and 1, p. 371. 
5. Butsculi, 0. — “ Zur Morphologie des Auges der Muscheln,” ‘ Verhandl. 
der Nat. -Med. Vereins zu Heidelberg,’ 1880, p. 175. 
6. Carriere, J. — ‘Die Sehorgane der Thiere,’ Muuchen u. Leipzig, 1885. 
7. De Graaf, H. W. — ‘ Bijdrage tot de Kennis van der Bouw eu de 
Ontwickeliug der Epiphyse bij Amphibien en Reptilicu,’ Leiden, 1886. 
8. De Graaf, H. W. — “ Zur Anatomie u. Entwickelung der Epiphyse bei 
Amphibien u. Reptilien,” ‘ Zool. Anz.,’ March 29th, 1886. 
9. Gunther, A. — ‘The Study of Fishes,’ 1880. 
10. Heape, W. — “The Development of the Mole,” ‘Quart. Journ. Micr. 
Sci.,’ Oct., 1886, p. 123. 
11. Hoffmann, C. K. — “ Weitere Untersuchungen zur Entwickelungsgesch. 
der Reptilien,” ‘ Morphol. Jahrb.,’ Bd. xi, 1885. 
12. Julin, Ch. — “ De la signification morphologique dc l’epiphyse des Verte- 
xes” (a compilation), ‘Bull. Scieutif. du Departement du Nord,’ 
Paris, 2me Serie, Xme Annee, 1887. 
13. Leydig, F. von.— “ D as Parietalorgan der Wirbclthiere,” ‘Zool. Anz.,’ 
No. 202, Oct. 10th, 1887, p. 531. 
